Refrigerating apparatus



May 15, 1956 H GRENELL 2,745,936

REF RIGERATING APPARATUS Filed Jan. 19, 1953 Fig.

INVENTOR. Le/and H. Grenel/ B Fig. 3 @mmmyg United States Patent 2,745,936 REFRIGERATING APPARATUS Leland H. Grenell, Oakwood, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application January 19, 1953, Serial No. 332,057 1 Claim. (Cl. 219-42) This invention relates to refrigerating apparatus and more particularly to a plate type heat exchanger and to the method of manufacturing the same.

It has been found that moisture will enter any unsealed crevices adjacent the outer edges of plate type evaporators and will tend to expand the crevices in response to alternate thawing and freezing such as encountered in repeatedly defrosting the evaporators. These crevices are commonly called frost blisters and frequently serve to create leaks in the evaporators after the evaporators have been in use for some time. It is an object of this invention to provide an improved method of manufacturing heat exchangers so as to prevent the formation of such frost blisters.

This invention relates to an improvement over the method shown in Towner Patent 2,250,172. As indicated by this patent, heat exchangers have been made from sheets of metal such as brass which have been brazed to one another so as to form a heat exchanger having suitable fluid passages between the sheets.

It is a further object of this invention to provide a simple and inexpensive arrangement for rebrazing edge portions of a plate type heat exchanger without the need for adding thereto any brazing material.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure l is a plan view of a plate type heat exchanger;

Figure 2 is a fragmentary sectional view showing in somewhat exaggerated manner an imperfection in the evaporator; and,

Figure 3 is a view similar to Figure 2 but showing the imperfection being eliminated.

For purposes of illustrating this invention, reference will be made to a conventional plate type evaporator wherein the plates are made of brass preferably containing approximately 85% copper and zinc and the bonding material consists of 60% copper and 40% zinc, so as to provide a brazing material which will melt at a temperature below that at which the sheets will melt. The invention, however, is equally applicable to heat exchangers and bonding materials made from other metals and alloys. Thus, the same principle may be used in manufacturing aluminum or steel evaporators for example.

Referring now to the drawings wherein a preferred embodiment of the invention has been illustrated, reference numeral 10 designates the conventional sheet metal type evaporator which has been manufactured by the process fully set forth in Schweller Patent 2,067,208 to which reference is hereby made for a more complete description of the process and materials used in making the evaporators. For purposes of illustration there has been shown an evaporator of the type used in the food compartment of a modern household refrigerator.

Evaporators of this type have holes 12 punched therein for mounting the evaporator and additional holes 14 for attaching a secondary condenser (not shown) to the one side of the evaporator. It has been found that imperfections or voids in the bond between the plates forming the opposite walls of the heat exchanger can cause the heat exchanger to eventually develop leaks adjacent these holes which obviously cannot be detected by leak tests conducted before the evaporator has been in use.

Figure 2 of the drawing shows a typical example of a heat exchanger wherein two plates 16 and 18 have been bonded to one another by means of a brazing material 20 which is originally placed between the two plates 16 and 18 in sheet form. The sheet 20 is made coextensive with the plates and the assembly is originally heated to a temperature high enough to melt the bonding material but not high enough to melt the plates. In Figure 2 of the drawing there is shown a crevice or the beginning of a frost blister 22 adjacent one of the holes 14. This crevice forms an ideal pocket for the accumulation of condensate water which after repeated freezing and cooling causes the crevice to increase in size until a leak develops. Tests have indicated that these gaps are not formed because of any lack of bonding material but rather because of the lack of any pressure to hold the plates together during the brazing operation. Since it would be impractical to provide means for holding the plates together throughout the entire contactin area during the brazing operation and since it is not always practical to form the various mounting holes before the brazing operation, it is difiicult to prevent crevices at points where holes are to be punched after the plates have been brazed.

According to my invention the objectionable crevices can be removed by rebrazing the area of the plates 16 and 18 immediately adjacent the edges of the holes in the plate.

As shown in Figure 3 of the drawing, these areas may be rebrazed by placing a pair of electrodes 24 on opposite sides of the evaporator adjacent each hole and passing current between the electrodes. These electrodes are of the type commonly used in spot welding machines and serve to apply pressure and heat to opposite sides of the evaporator. The amount of heat applied is pref erably less than that required for welding the plates together but suificient to remelt the brazing material 20 with the result that the raw edges or crevices adjacent the holes in the plate are completely sealed. The above described process is referred to as resistance brazing as distinguished from resistance welding where the plates themselves are heated to a high enough temperature to actually produce welding of the plates.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claim which follows.

What is claimed is as follows:

The method of manufacturing plate type receptacles which comprises placing two complementary plates together with a fuseable bonding material between the two plates, heating the assembly to fuse the bonding material, allowing the plates to cool, and thereafter resistance brazing the area adjacent the edge portion of said plates to seal the edges so as to prevent the formation of frost blisters.

References Cited in the file of this patent UNITED STATES PATENTS 904,881 Lachman Mar. 24, 1908 1,056,061 Rogers Mar. 18, 1913 2,452,805 Sussenbach Mar. 2, 1948 

